A few key things are that the female needs to be in the right stage of heat and also needs to be brought into the males territory for mating and not the other way around. Male dogs become sexually mature around 6-7 months of age so he is old enough.
To breed successfully you need to understand the heat cycle. I have explained it below and included a site that has a pictorial guide, so there is no mistake what stage of heat your girl is in.
Female Dogs go into heat at any time between six and twelve months usually. The average heat cycle for a dog is approximately three weeks but for some dogs it is longer and for others it is shorter. Some as short as ten days and some as long as four weeks or more. Usually your dog will go into heat every six, seven months though again each dog is different and can go back into heat as early as four months or not for twelve months. Most however are average.
During the first part of a dogs heat period you will notice swelling of the vulva, possibly an increase in urination and bleeding. If there are male dogs around you will notice them hanging around her. This stage generally last about seven days and she will not allow males to mate with her during this period The second part of the heat cycle is when she will accept a male and breed. Usually bleeding has stopped or become straw colored at this point. This can last from four to twenty-one days though the average is seven days. Many expert say the ninth or tenth day of heat is the optimum day for breeding. It is during this period of time that you will want to allow mating. Most breeders allow the dogs to mate every other day during this period.
Then during the last stage of heat she will be less willing to breed as she is going out of heat. This stage can again last from four to twenty-one days as well but averages seven days.
Each dog is different so some evaluation by the owner is necessary. The whole heat period should be approximately twenty-one days but as stated can be longer or shorter depending on the dog.
Here is an excellent website with pictures to illustrate a female in different stages of heat.
There are mismated shots but they have been proven to cause an increase in dogs developing uterine infections and requiring spaying as a result, so they are not recommended. In addition, a diaper is not going to stop a male from mating with your female. One of the dogs will remove it to mate. If the dogs are not kept apart, then there is a strong possibility that she will get pregnant. You will need to isolate her or the males. Many owners send the male to caring relatives or board the male for that duration.
I hope you find this information helpful.